1. Field of the Invention
The present invention relates to an oxide semiconductor based thin-film transistor and a method for manufacturing the same, and more particularly to an oxide semiconductor based thin-film transistor with an intermediate barrier layer for improving reliability of the thin-film transistor.
2. Description of the Related Art
Recently, with growing interest in information displays and an increasing demand for portable electronic devices, light and thin-film type flat panel display (FPD) devices have been widely studied and commercialized. In particular, among the flat panel displays, liquid crystal display (LCD) devices and organic light-emitting display (OLED) devices have been widely studied, and a thin-film transistor (TFT) has been used as a switching element and/or a driving element in the LCD device and the OLED device.
The thin-film transistor is classified into a thin-film transistor using amorphous-silicon, a thin-film transistor using poly-silicon and a thin-film transistor using an oxide semiconductor according to materials used as an active layer. When the thin-film transistor using poly-silicon is manufactured, a process for implanting ions to adjust resistance of the active layer is further performed, and an ion implantation process using an additional mask for defining an ion implantation region is further performed. For this reason, there is a disadvantage in process. The thin-film transistor using an oxide semiconductor has higher mobility than that of the thin-film transistor using amorphous-silicon semiconductor. Further, the thin-film transistor with an oxide semiconductor generally exhibit lower leakage current than the thin-film transistor with amorphous-silicon semiconductor and poly-silicon semiconductor, and reliability of the thin-film transistor using an oxide semiconductor is relatively higher than those of the thin-film transistor using amorphous silicon and the thin-film transistor using poly-silicon. Furthermore, the thin-film transistor using an oxide semiconductor has an advantage in that uniform distribution characteristics of a threshold voltage are obtained as compared to the thin-film transistor using poly-silicon.
During the operation of the oxide semiconductor based TFT, carriers have a tendency to be accumulated in the insulation layer and to remain “trapped” in the insulation layer throughout the operation of the TFT. Some of the trapped carriers remain in the insulation layer even after the TFT is turned off. In most instances, once carriers are trapped, they remain trapped throughout the on and off states of the TFT, possibly for the entire life of the TFT. This “trapping” of carriers causes the threshold voltage to gradually shift, and the amount of threshold shift is generally correlated to the amount of deep trap density.